For many lighting applications, it is desirable to have an illumination source that produces a light beam having a variable angular distribution. Variability is desired, for example, to create a wide-angle light beam for illuminating an array of objects, or a narrow-angle beam for illuminating a single, small object. Conventionally, the angular distribution is varied by moving the light source(s) toward or away from the focal point of a lens or parabolic mirror. As the light source is moved away from the focal point, its image is blurred, forming a wider beam. Unfortunately, in doing so, the image is degraded, becoming non-uniform; in the case of the familiar parabolic reflector used in flashlights, a dark “donut hole” is formed, which is visually undesirable and sacrifices full illumination of the scene. Furthermore, moving the lens often reduces the collection efficiency of the lens, as light that is not refracted by a lens or reflected by a reflector surface is lost.
Because of these optical artifacts and efficiency losses, most light sources use a single, fixed lens. For light bulbs such as, e.g., MR-16 halogen bulbs, several different types of optics are manufactured to create beams of various beam divergences, ranging from narrow beam angles (“spot lights”) to wide angles (“flood lights”), with various degrees in between. Unless the user maintains different light bulbs on hand to accommodate all potentially desired beam divergences, however, he or she will generally be limited to one or a small number of alternatives. Traveling with an assortment of bulbs for portable light sources is even less realistic. As a result, users often tolerate either a source ill-suited to changing or unexpected conditions, or the poor optical quality of light sources with variable beam optics. A need, therefore, exists for light sources that produce variable beam angles without sacrificing beam quality and/or provide other novel and innovative features.